Forward Error Correction Coding For AM 9kHz and 10kHz In-Band On-Channel Digital Audio Broadcasting Systems

ABSTRACT

A method of broadcasting an AM compatible digital audio broadcasting signal includes: producing an analog modulated carrier signal centrally positioned in a radio channel, wherein the analog modulated carrier signal is modulated by an analog signal, producing a plurality of digitally modulated subcarrier signals in the radio channel, wherein the digitally modulated subcarrier signals are modulated using complementary pattern-mapped trellis code modulation (CPTCM) including a code mapped to overlapping partitions including an upper main partition, a lower main partition, an upper backup partition and a lower backup partition, and a non-overlapping tertiary partition, and transmitting the analog modulated carrier signal and the plurality of digitally modulated subcarrier signals. Transmitters that broadcast the signal and receivers that receive the signal, and the reception method are also included.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/764,629, for “Forward Error Correction Coding For Hybrid AMIn-Band On-Channel Digital Audio Broadcasting Systems”, filed Jan. 26,2004, which is hereby incorporated by reference.

FIELD OF THE INVENTION

This invention relates to methods and apparatus for digital audiobroadcasting, and more particularly to such methods and apparatus forbroadcasting AM compatible in-band on-channel (IBOC) digital audiobroadcasting (DAB) signals.

BACKGROUND OF THE INVENTION

Digital audio broadcasting (DAB) is a medium for providingdigital-quality audio, superior to existing analog broadcasting formats.AM in-band, on-channel (IBOC) DAB can be transmitted in a hybrid formatwhere a digitally modulated signal coexists with the AM signal, or itcan be transmitted in an all-digital format where the removal of theanalog signal enables improved digital coverage with reducedinterference. The hybrid format allows existing receivers to continue toreceive the AM signal while allowing new IBOC receivers to decode theDAB signal. IBOC DAB requires no new spectral allocations because eachDAB signal is simultaneously transmitted within the spectral mask of anexisting AM channel allocation. IBOC DAB promotes economy of spectrumwhile enabling broadcasters to supply digital quality audio to theirpresent base of listeners.

U.S. Pat. No. 5,588,022 teaches a method for simultaneously broadcastinganalog and digital signals in a standard AM broadcasting channel. TheDAB signal comprises an amplitude modulated radio frequency signalincluding a first subcarrier modulated by an analog program signal andhaving a first frequency spectrum, and a plurality of digitallymodulated subcarrier signals that are broadcast within a bandwidth thatencompasses the first frequency spectrum. The digitally modulatedsubcarrier signals are modulated by a digital program signal. A firstgroup of the digitally modulated subcarrier signals lies within thefirst frequency spectrum and is modulated in quadrature with the firstsubcarrier signal. Second and third groups of the digitally modulatedsubcarrier signals lie outside of the first frequency spectrum and aremodulated both in-phase and in-quadrature with the first subcarriersignal. U.S. Pat. No. 6,243,424 discloses another embodiment of an AMDigital Audio Broadcasting system.

A method and apparatus for forward error correction coding for an AMin-band on-channel (IBOC) digital audio broadcasting (DAB) system isdescribed in U.S. Pat. No. 6,523,147, the disclosure of which is herebyincorporated by reference. A digital audio broadcasting method usingpuncturable convolutional code is described in U.S. Pat. Nos. 6,108,810and 6,345,377, the disclosures of which are hereby incorporated byreference.

The present invention seeks to provide an AM IBOC DAB signal that canaccommodate various interference scenarios as well as transmitters andreceivers that utilize the signal.

SUMMARY OF THE INVENTION

In a first aspect, the invention provides a method of broadcasting an AMcompatible digital audio broadcasting signal. The method includes:producing an analog modulated carrier signal centrally positioned in aradio channel, wherein the analog modulated carrier signal is modulatedby an analog signal, producing a plurality of digitally modulatedsubcarrier signals in the radio channel, wherein the digitally modulatedsubcarrier signals are modulated using complementary pattern-mappedtrellis code modulation (CPTCM) including a code mapped to overlappingpartitions including an upper main partition, a lower main partition, anupper backup partition and a lower backup partition, and anon-overlapping tertiary partition, and transmitting the analogmodulated carrier signal and the plurality of digitally modulatedsubcarrier signals.

In another aspect, the invention provides a transmitter for broadcastingan AM compatible digital audio broadcasting signal. The transmitterincludes a processor for modulating a plurality of subcarriers usingcomplementary pattern-mapped trellis code modulation (CPTCM) including acode mapped to overlapping partitions including an upper main partition,a lower main partition, an upper backup partition and a lower backuppartition, and a non-overlapping tertiary partition, and a transmitterfor transmitting an analog modulated carrier signal and the plurality ofdigitally modulated subcarrier signals.

In another aspect, the invention provides a method of receiving an AMcompatible digital audio broadcasting signal. The method includes:receiving an analog modulated carrier signal centrally positioned in aradio channel, and a plurality of digitally modulated subcarrier signalsin the radio channel, wherein the digitally modulated subcarrier signalsare modulated using complementary pattern-mapped trellis code modulation(CPTCM) including a code mapped to overlapping partitions including anupper main partition, a lower main partition, an upper backup partitionand a lower backup partition, and a non-overlapping tertiary partition,and demodulating the analog modulated carrier signal and the pluralityof digitally modulated subcarrier signals; and producing an outputsignal in response to the demodulating step.

In another aspect, the invention provides a receiver receiving an AMcompatible digital audio broadcasting signal. The receiver includes aninput for receiving an analog modulated carrier signal centrallypositioned in a radio channel, and a plurality of digitally modulatedsubcarrier signals in the radio channel, wherein the digitally modulatedsubcarrier signals are modulated using complementary pattern-mappedtrellis code modulation (CPTCM) including a code mapped to overlappingpartitions including an upper main partition, a lower main partition, anupper backup partition and a lower backup partition, and anon-overlapping tertiary partition; a demodulator for demodulating theplurality of subcarriers with the partitioned bits; and an output forproducing an output signal in response to the demodulator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of partition and subcarrierassignments for a hybrid AM IBOC DAB signal in accordance with thisinvention.

FIG. 2 is a functional block diagram of an AM IBOC DAB transmitterconstructed in accordance with this invention.

FIG. 3 is a block diagram illustrating the functionality of forwarderror correction (FEC) and interleaving for a 20 or 30 kHz AM IBOCsystem.

FIG. 4 is a block diagram illustrating the functionality of IBOC dataservice (IDS) channel FEC and interleaving for a 20 or 30 kHz AM IBOCsystem.

FIG. 5 is a functional block diagram of an AM IBOC DAB receiverconstructed in accordance with this invention.

FIG. 6 is a block diagram illustrating the functionality of adeinterleaver and FEC decoder for a 20 or 30 kHz AM IBOC system.

FIG. 7 is a block diagram illustrating the functionality of IDS channeldeinterleaver and FEC decoder for a 20 or 30 kHz AM IBOC system.

FIG. 8 is a diagram of a robust soft metric F(y) for 4-ASK (I or Qcomponent of 16-QAM).

FIG. 9 is a diagram of a robust soft metric F(y) for BPSK (I or Qcomponent of QPSK).

FIG. 10 is a schematic representation of the subcarrier assignments foran AM hybrid in-band on-channel digital audio broadcasting systemcompatible with 9 kHz channel spacing.

FIG. 11 is a schematic representation of the subcarrier assignments foran AM hybrid in-band on-channel digital audio broadcasting systemcompatible with 10 kHz channel spacing.

FIG. 12 is a block diagram illustrating the functionality of the forwarderror correction (FEC) and interleaver for a 24-kbps single stream AMIBOC system.

FIG. 13 is a block diagram illustrating the functionality of a forwarderror correction (FEC) interleaver for an integrated digital services(IDS) channel in an AM IBOC system.

FIG. 14 is a simplified block diagram of relevant portions of an IBOCDAB receiver which can receive signals coded in accordance with themethod of the present invention.

FIG. 15 is a block diagram illustrating the functionality of an AM IBOChybrid deinterleaver and FEC decoder implementation that permits rapidacquisition of the audio information.

FIG. 16 is a block diagram illustrating the functionality of another AMIBOC hybrid deinterleaver and FEC decoder.

FIG. 17 is a plot illustrating Average White Gaussian Noise (“AWGN”)performance of all partitions compared to current core and enhancedcoverage.

FIG. 18 is a plot illustrating AWGN performance in the presence of astrong second adjacent hybrid interferer.

DETAILED DESCRIPTION OF THE INVENTION 20 kHz or 30 kHz Bandwidth System

In one aspect, this invention provides a single stream hybrid AM IBOCDAB system having a 20 or 30 kHz bandwidth and 25 and 19 kbps modes. Thesystem broadcasts a waveform including an analog modulated carrier and aplurality of digitally modulated subcarriers in the same channel as theanalog modulated carrier. The digital signal is divided into severalpartitions, which are mapped to groups of the subcarriers. Referring tothe drawings, FIG. 1 is a schematic representation of the partition andsubcarrier assignments for a hybrid 20 or 30 kHz AM IBOC signal.

The signal 10 includes an analog modulated carrier signal 12 that ismodulated by an analog signal, resulting in an AM host signal generallyindicated by line 14. The signal further includes a plurality ofsubcarriers at evenly spaced positions (numbered −81 to +81, andspanning a bandwidth of about 30 kHz) in the radio channel 16. BPSKmodulated timing subcarriers 18 and 20 are located at the subcarrierpositions +1 and −1, closest to the analog modulated carrier. A firstplurality of subcarrier signals 22 are located at positions 2 through 31in a first portion 24 of the radio channel and a second plurality ofsubcarrier signals 26 are located at positions −2 through −31 in asecond portion 28 of the radio channel. The first and second pluralitiesof subcarrier signals are complementary modulated QPSK subcarriersignals and have a power spectral density below the analog modulatedcarrier by at least a first margin.

A third plurality of subcarrier signals 30 are located at positions 32through 36 in a third portion 32 of the radio channel and a fourthplurality of subcarrier signals 34 are located at positions −32 through−36 in a fourth portion 36 of the radio channel. The third and fourthpluralities of subcarrier signals are complementary modulated 16-QAMsubcarrier signals and have a power spectral density below the analogmodulated carrier by at least a second margin. Complementary modulatedsubcarriers in the lower sideband groups 26 and 34 are modulated as themirror image (negative complex conjugate) of corresponding subcarriersin the upper sideband groups 22 and 30.

A fifth plurality of subcarrier signals 38 are located at positions 37through 51 in a fifth portion 40 of the radio channel and a sixthplurality of subcarrier signals 42 are located at positions −37 through−51 in a sixth portion 44 of the radio channel. The fifth and sixthpluralities of subcarrier signals are 16-QAM modulated signals and havea power spectral density below the analog modulated carrier by at leasta third margin. In one embodiment, the first margin is 50 dBc, thesecond margin is 43 dBc, and the third margin is 40 dBc.

The first, second, third, fourth, fifth and sixth pluralities ofsubcarrier signals are modulated by one or more digital signals. Thedigital signals can include a digital version of a program signal usedto modulate the analog modulated carrier, as well as other digitalsignals.

An optional seventh plurality of subcarrier signals 46 can be located atpositions 57 through 81 in a seventh portion 48 of the radio channel,and an optional eighth plurality of subcarrier signals 50 can be locatedat positions −57 through −81 in an eighth portion 44 of the radiochannel. The seventh and eighth pluralities of subcarrier signals are16-QAM modulated signals and have a power spectral density below theanalog modulated carrier by at least the third margin. The subcarriersin the fifth, sixth, seventh and eighth portions of the channel are notcomplementary modulated.

An IBOC Data Service (IDS) subcarrier 52 is located at position 52between the fifth and seventh pluralities of subcarriers, and an IBOCData Service subcarrier 54 is located at a position −52 between thesixth and eighth pluralities of subcarriers. In one embodiment, the IBOCData Service subcarriers have a power spectral density at least 40 dBcbelow the analog modulated carrier. The subcarriers at locations 53-56are omitted because of first adjacent channel interference.

The AM IBOC DAB signal subcarriers are digitally modulated using COFDM(Coded Orthogonal Frequency Division Multiplexing). Each of thesubcarriers is modulated using 16-QAM, QPSK or BPSK (subcarriers ±1only) symbols. The digital information (e.g., audio) is forward errorcorrected (FEC) coded using complementary pattern-mapped trellis codedmodulation (CPTCM), and then separated into partitions that areinterleaved separately. The CPTCM method of FEC for the AM IBOC is basedupon a combination of a code pattern-mapping technique described below,and the application of overlapping Complementary Puncture Codes to AMIBOC systems.

The partitions are identified by letters in FIG. 1. The digitalinformation in partition C is used to modulate the first and secondpluralities of subcarriers. The digital information in partition B isused to modulate the third and fourth pluralities of subcarriers. Thedigital information in partition AU is used to modulate the fifthplurality of subcarriers. The digital information in partition AL isused to modulate the sixth plurality of subcarriers. The digitalinformation in partition XU is used to modulate the seventh plurality ofsubcarriers. The digital information in partition XL is used to modulatethe eighth plurality of subcarriers. The partitions are mapped tosubcarriers at particular power levels to minimize both hostinterference and interference to adjacent channels, while attempting tomaximize coverage. Different interference scenarios will causecorruption to different partitions. The goal of the CPTCM coding andgrouping into these partitions is to maximize coverage while minimizinginterference.

The basic requirements for the CPTCM code include the ability topuncture the original code and map the code bits to the symbols in amanner that provides superior coding gain over a random mapping of thecode bits. The CPTCM code must further include the ability to puncturethe original code in various overlapping partitions including Main,Backup, Lower Sideband and Upper Sideband. Each of the overlappingpartitions must survive as a good code as designed for typicalinterference and AM channel conditions. Partitions AL, AU, B and C formthe Main component, while the optional XL and XU partitions form theBackup which is time diverse from the Main component. Furthermore, thelower AL and XL partitions can be completely corrupted while the AU andXU partitions can carry the signal. Similarly, the upper AU and XUpartitions can be completely corrupted while the AL and XL partitionscan carry the signal. The inner B and C partitions add coding gain tothe A and X partitions. Various levels of corruption can be tolerated inlikely interference scenarios.

FIG. 2 is a block diagram of a DAB transmitter 60 that can broadcastdigital audio broadcasting signals in accordance with the presentinvention. A signal source 62 provides the signal to be transmitted. Thesource signal may take many forms, for example, an analog program signaland a digital program signal, and/or one or more other digitalinformation signals. A digital signal processor (DSP) based modulator 64processes the source signal in accordance with various signal processingtechniques, such as source coding, interleaving and forward errorcorrection, to produce in-phase and quadrature components of the complexbase band signal on lines 66 and 68. These components are shifted up infrequency, filtered and interpolated to a higher sampling rate inup-converter block 70. This produces digital samples at a rate f_(s), onintermediate frequency signal f_(if) on line 72. Digital-to-analogconverter 74 converts the signal to a plurality of digitally modulatedsubcarriers on line 76. The digitally modulated subcarriers are combinedwith an analog modulated signal 78 as illustrated by summation point 80.An intermediate frequency filter 82 rejects alias frequencies to producethe intermediate frequency signal f_(if) on line 84. A local oscillator86 produces a signal f_(lo) on line 88, which is mixed with theintermediate frequency signal on line 84 by mixer 90 to produce sum anddifference signals on line 92. Unwanted intermodulation components andnoise are rejected by image reject filter 94 to produce the compositesignal f_(c) on line 96. A high power amplifier 98 then sends thissignal to an antenna 100, which serves as a means for broadcasting thecomposite signal. The composite broadcast signal is shown in FIG. 1.

The Forward Error Correction (FEC) technique used in the AM IBOC(In-Band On-Channel) DAB (Digital Audio Broadcast) system of thisinvention is referred to as Complementary Pattern-mapped Trellis-CodedModulation (CPTCM). CPTCM coding is designed to be compatible with thehost analog signal and to accommodate the likely interference scenariosencountered in the AM IBOC channel. One particular mode of operation isintended for a single stream (25.8 or 19.3 kbps) of digital audio thatcan be broadcast within a 20 kHz RF bandwidth. The 25.8 kbps mode has anoptional Backup extension partition in the outer portions of thesidebands, expanding the bandwidth to 30 kHz while providingLower/Upper/Main/Backup diversity. The 20 kHz RF bandwidth mode reducesinterference and has no second-adjacent channel interference issuesrelative to the 30 kHz mode. However, digital coverage and robustnessare reduced relative to the 30 kHz mode, since there are insufficientcode bits to accommodate Main/Backup diversity. The CPTCM code techniquepartitions a “mother code” into smaller code partitions in a mannerwhich is much better than random interleaving.

Functional block diagrams illustrating the assembly and partitioning ofinformation bits is shown in FIGS. 3 and 4. FIG. 3 is a block diagramillustrating the functionality of forward error correction (FEC) andinterleaving for a 20 or 30 kHz AM IBOC system. Data to be transmittedis received as indicated by arrow 101. Block 102 shows that the data isassembled into modem frames containing either 38,400 bits for rate 4/5coding, or 28,800 bits for rate 3/5 coding. Block 104 shows that thedata in each modem frame is divided into groups. For rate 4/5 coding,the groups have 8 bits, and for rate 3/5 coding, the groups have 6 bits.Forward error correction encoding and puncturing is then performed asshown in block 106. This produces 4800 10-bit outputs for both rates ⅘and ⅗, and if the optional 30 kHz waveform is used, additional code bitsat rate 4/5 for partitions XU and XL. The forward error corrected datais then assigned to partitions as illustrated by blocks 108, 110, 112,114, 116 and 118. The numbers on the output arrows of block 106represent the number of code bits mapped into the partitions for eachpuncture period.

The partitioned data is then mapped to the interleaver partitions. Thedata in partitions XU and XL is delayed as shown by blocks 120 and 122to provide time diversity. The complementary feature of the FEC code isnot present with the 20 kHz modes since the code rate is greater thanR=½. However, the complementary feature is always used for the IBOC DataService (IDS) subcarriers. The mother code is partitioned into a pair ofcomplementary codes. For example a rate 1/3 code can be partitioned intoa pair of good rate 2/3 codes, where each rate 2/3 code is designed tohave good similar properties. Conversely if the r=⅓ code is randomlypartitioned by an interleaver, then the resulting r=⅔ codes will likelybe poor and catastrophic.

Two code rates are provided to allow a tradeoff between higherthroughput (FEC rate 4/5 yields 25.8 kbps) or greater coverage (FEC rate3/5 yields 19.3 kbps). The extended 30 kHz version of the R=⅘ coderesults in a R=⅖ code after code combining at the receiver to provideall the properties of the CPTCM technique with Lower/Upper/Main/Backupdigital diversity. The 20 kHz version of the R=⅘ code provides the Mainchannel only and employs time diversity with the analog signal. Themodulation and interleaving for the two rates are identical, althoughthe information rates and code puncture patterns differ. In the absenceof interference issues, a broadcaster would choose the 30 kHz optionusing the XL and XU partitions yielding coding gain and Backupdiversity. However if a first or second adjacent signal would beaffected in its coverage area, then that particular XL or XU sidebandmay be suppressed to avoid interference. A 20 kHz signal would resultwhen both XL and XU are suppressed. Although the 20 kHz signal inflictsmuch lower interference, its coverage is less.

FIG. 4 is a block diagram illustrating the functionality of an IBOC dataservice (IDS) channel FEC and interleaving for 20 or 30 kHz AM IBOCsystem. Data to be transmitted in the data service channel is receivedas indicated by arrow 130. Block 132 shows that the data is assembledinto an IDS block of 80 bits. Block 134 shows that the data in each IDSblock is divided into 4-bit groups. Forward error correction encodingand puncturing is then performed as shown in block 136. This produces12-bit outputs. The forward error corrected data is assigned to theupper and lower IDS subcarriers as illustrated by blocks 138 and 140.The data is then mapped to the IDS interleaver partitions.

The CPTCM technique is applied to Quadrature Amplitude Modulated (QAM)symbols by treating the I and Q components as independently codedAmplitude Shift Keying (ASK) signals. Specifically the 16-QAM symbol iscreated by modulating the I or Q component with independent 4-ASKsignals. The 4-ASK symbols are generated from specially selected 2-bitgroups which are then used to address the Gray-mapped constellationpoints. The mapping of the code bit pairs to the 4 levels of the 4-ASKsymbols is presented in Table 1. The Quadrature Phase Shift Keying(QPSK) modulation is conventional assuming Binary Phase Shift Keying(BPSK) in each of the two dimensions.

TABLE 1 Mapping of CPTCM-coded bits to 4 levels of the 4-ASK symbols(for each 16-QAM dimension). Level Level Level Level MAPPING −1.5 −0.5+0.5 +1.5 A = MSB 0 0 1 1 B = LSB 0 1 1 0 A/B indicate MSB/LSB only, andare not Partitions

The FEC code and interleaver are designed for CPTCM with a nominal 25 or19 kbps single stream audio codec. The interleaved symbols are mappedonto a group of 30 QPSK complementary subcarrier pairs in the 0 to ±6kHz region, 5 16-QAM complementary subcarrier pairs in the 6 to 7 kHzand −6 to −7 kHz regions, and 15 16-QAM noncomplementary subcarriers ineach of the 7 to 10 kHz and −7 to −10 kHz regions. An optional 25subcarriers are transmitted in each of the 10 to 15 kHz and −10 to −15kHz regions for the optional 30 kHz R=⅘ partitions. The partition codebits that are mapped onto these subcarriers are defined below. The QPSKsubcarriers are complementary, meaning that the lower QPSK group ismodulated as the mirror image (negative complex conjugate) of the UpperQPSK group. Furthermore, the inner 10 16-QAM subcarriers in the 6 to 7kHz and −6 to −7 kHz regions are complementary, while the remainingouter 16-QAM subcarriers are independent (noncomplementary). Twoadditional outer subcarriers located at about ±9.45 kHz are used for IDSinformation. FIG. 1 illustrates the placement of these subcarrierswithin the 20 kHz (or optional extended 30 kHz) bandwidth.

The CPTCM code is created through puncturing of a rate 1/3 convolutionalcode. The FEC code requires appropriate puncture patterns and code-bitmapping to provide good results. The puncture pattern assigns code bitsfor the groups of subcarrier partitions. The combined puncture patternsfor the partitions of the FEC codes for the two rates of the MainProgram Audio (MPA) information is defined in Tables 2a and 2b. Thesubscripts in Tables 2a and 2b represent the code bits in the partition.Subscripts are used because there may be more than one code bit. Forexample, there is only one B bit, but there are three C bits.

TABLE 2a Puncture pattern bit assignments for R = 4/5 FEC code (R = 2/5w/Backup). C₀ 0 AU₀ XU₃ C₁ 0 AL₂ XL₃ AL₀ XL₁ 0 AL₁ AU₁ XU₁ 0 AU₂ XL₀ BXL₂ XL₄ XU₀ C₂ XU₂ XU₄

The FEC 20 kHz Main (A,B,C) Puncture Pattern using convolutional codegenerator G=[G1=561o, G2=753o, G3=711o] (where o denotes octal notation)has a Hamming free distance of d_(f)=5 and the number of paths at thatdistance is a=4. The B and C partitions are complementary modulated (notto be confused with complementary code) meaning that the lowersubcarrier is the negative complex conjugate of the corresponding uppersubcarrier. Therefore the upper and lower groups of subcarriers are notindependent. The 30 kHz Backup (X) Puncture Pattern has d_(f)=5 and a=7.The Composite R=⅖ Puncture Pattern has d_(f)=12 and a=2.

TABLE 2b Puncture pattern bit assignments for R = 3/5 FEC code. AL₀ AU₀AL₁ AU₁ AL₂ AU₂ C₀ B 0 C₁ C₂ 0 0 0 0 0 0 0The FEC Composite Puncture Pattern using G=[G1=561o, G2=753o, G3=711o]has d_(f)=8 and a=1.

The IDS subcarriers are modulated using 16-QAM symbols. Subcarriers −52and +52 are the IDS subcarriers. The IDS Sequence is 32 symbols long(symbols 0 through 31) and associated with a block length. Symbolstransmitted on subcarriers at locations 11 and 27 are assigned asTraining Symbols. The remaining 30 symbols carry 120 code bits of rate2/3 coded information. Hence each IDS Sequence carries 80 informationbits, including an 8-bit CRC. A rate 1/3 code is employed with rate 2/3complementary components. The combined puncture patterns for thepartitions of the FEC codes for the IDS information is defined in Table3.

TABLE 3 Puncture pattern bit assignments for IDS Lower and Uppersubcarriers. L₀ U₄ L₄ U₀ L₂ U₃ L₃ U₂ U₁ L₁ U₅ L₅The IDS FEC Composite Puncture Pattern using G=[G1=561o, G2=753o,G3=711o] has d_(f)=17 and a=3. For either the Lower or Upper IDSpartition the IDS FEC Puncture Pattern has d_(f)=7 and a=6.

The interleavers for the Single Stream Main Program Audio (MPA) span anentire Modem Frame consisting of 256 COFDM symbols (bauds). The IDSinterleavers span one block of 32 COFDM symbols, where there are 8blocks in a Modem Frame.

The interleaving for the MPA code bits is separated into 6non-overlapping partitions. The Partition C spans 30 complementary QPSKsubcarrier pairs 2 through 31 and −2 through −31. The Partition B spans5 complementary 16-QAM subcarrier pairs 32 through 36 and −32 through−36. The Partition AU spans 15 non-complementary 16-QAM subcarriers 37through 51. The Partition AL spans 15 non-complementary QPSK subcarriers−37 through −51. The optional 30 kHz Partition XU spans 25non-complementary 16-QAM subcarriers 57 through 81. The optional 30 kHzPartition XL spans 25 non-complementary QPSK subcarriers −57 through−81. The IDS is split between two Partitions IDSL and IDSU mapped tosubcarriers −52 and +52. The MPA interleaver expressions span the entireModem Frame of 256 OFDM symbols (Block of 32 symbols for IDS), while thespan over the number of subcarriers is dependent on the size of thepartition. For example, the code bits are mapped over the subcarriers ina partition, that is, the code bits span the partition.

The MPA interleaving is performed after gathering one Modem Frame of MPAdata. The data in one embodiment consists of 38400 bits for the rate 4/5mode, or 28800 bits for the rate 3/5 mode. The data is then coded,punctured, and grouped into partitions AL, AU, B and C for subsequentinterleaving. The partition bits within each puncture pattern areordered as indicated, then stacked over the multiple puncture patternscomprising the Modem Frame. The ordering of the code bits within eachpartition ensures that the code bits are mapped to the particular QAM orQPSK symbol bits per the interleaver expressions.

The 80 IDS information bits comprising each Block are coded andassembled in groups of bits from the puncture patterns. The groupingswithin each partition are mapped using the interleaver expressionspresented in Table 4.

In Table 4, the value of n indicates the particular ordered code bit(one of N bits) within each partition. The index k is computed from n,and points to one of the symbol locations within the Modem Frame (orBlock for the IDS) identifying the row and column within the partition.Each of the 16-QAM symbols carries 4 code bits, while each QPSK symbolcarries 2 bits. The value of p in the interleaver expression indicatesthe particular bit within each symbol (i.e., I or Q, and MSB or LSBwhere applicable).

TABLE 4 Interleaver Mapping for all Partitions. P code bit PartitionIndex k Row & column locations for symbol k in symbol AU_(k,,p)N = 14400k = mod[n + floor(n/3600), 3600]n = 0 . . . N − 1 $\begin{matrix}{{{rowA}(k)} = {{mod}\left( {{5 + {109 \cdot k} + {11 \cdot {{floor}\left( \frac{7 \cdot k}{15} \right)}} + {111 \cdot {{floor}\left( \frac{k}{240} \right)}}},256} \right)}} \\{{{{{colA}(k)} = {{mod}\left( {{7 \cdot k},15} \right)}};{\mspace{11mu} \;}{k = {0\mspace{14mu} \ldots \mspace{14mu} 3599}}},} \\{{{Training}\mspace{14mu} {symbols}\mspace{14mu} {at}\mspace{14mu} {locations}\mspace{14mu} k} = {3600\mspace{14mu} \ldots \mspace{14mu} 3839}}\end{matrix}\quad$ p = mod(n, 4) AL_(k,,p)N = 14400 k = mod[n +floor(n/3600), 3600]n = 0 . . . N − 1 $\begin{matrix}{{{rowA}(k)} = {{mod}\left( {{5 + {109 \cdot k} + {11 \cdot {{floor}\left( \frac{7 \cdot k}{15} \right)}} + {111 \cdot {{floor}\left( \frac{k}{240} \right)}}},256} \right)}} \\{{{{{colA}(k)} = {{mod}\left( {{7 \cdot k},15} \right)}};{\mspace{11mu} \;}{k = {0\mspace{14mu} \ldots \mspace{14mu} 3599}}},} \\{{{Training}\mspace{14mu} {symbols}\mspace{14mu} {at}\mspace{14mu} {locations}\mspace{14mu} k} = {3600\mspace{14mu} \ldots \mspace{14mu} 3839}}\end{matrix}\quad$ p = mod(n, 4) B_(k,,p)N = 4800 k = mod[n +floor(n/1200), 1200]n = 0 . . . N − 1 $\begin{matrix}{{{rowB}(k)} = {{mod}\left( {{14 + {102 \cdot k} + {25 \cdot {{floor}\left( \frac{2 \cdot k}{5} \right)}} + {111 \cdot {{floor}\left( \frac{k}{80} \right)}}},256} \right)}} \\{{{{{colB}(k)} = {{mod}\left( {{2 \cdot k},5} \right)}};{\mspace{11mu} \;}{k = {0\mspace{14mu} \ldots \mspace{14mu} 1199}}},} \\{{{Training}\mspace{14mu} {symbols}\mspace{14mu} {at}\mspace{14mu} {locations}\mspace{14mu} k} = {1200\mspace{14mu} \ldots \mspace{14mu} 1279}}\end{matrix}\quad$ p = mod(n, 4) C_(k,,p)N = 14400 k = mod[n +floor(n/7200), 7200]n = 0 . . . N − 1 $\begin{matrix}{{{rowC}(k)} = {{mod}\left( {{4 + {97 \cdot k} + {6 \cdot {{floor}\left( \frac{19 \cdot k}{30} \right)}} + {111 \cdot {{floor}\left( \frac{k}{480} \right)}}},256} \right)}} \\{{{{{colC}(k)} = {{mod}\left( {{19 \cdot k},30} \right)}};{\mspace{11mu} \;}{k = {0\mspace{14mu} \ldots \mspace{14mu} 7199}}},} \\{{{Training}\mspace{14mu} {symbols}\mspace{14mu} {at}\mspace{14mu} {locations}\mspace{14mu} k} = {7200\mspace{14mu} \ldots \mspace{14mu} 7679}}\end{matrix}\quad$ p = mod(n, 2) IDSU_(k,,p) k = mod[n + floor(n/60),30] rowIDS(k) = mod(5 + 9 · k, 32) p = mod(n, 4) N = 120 n = 0 . . . N −1 colIDS(k) = 0; k = 0 . . . 29, Training symbols at locations 11 and 27IDSL_(k,,p) k = mod[n + floor(n/60), 30] rowIDS(k) = mod(5 + 9 · k, 32)p = mod(n, 4) N = 120 n = 0 . . . N − 1 colIDS(k) = 0; k = 0 . . . 29,Training symbols at locations 11 and 27 XU_(k,,p)optionalN = 24000 k =mod[n + floor(n/6000), 6000]n = 0 . . . N − 1 $\begin{matrix}{{{rowA}(k)} = {{mod}\left( {{1 + {99 \cdot k} + {29 \cdot {{floor}\left( \frac{9 \cdot k}{25} \right)}} + {111 \cdot {{floor}\left( \frac{k}{400} \right)}}},256} \right)}} \\{{{{{colA}(k)} = {{mod}\left( {{9 \cdot k},25} \right)}};{\mspace{11mu} \;}{k = {0\mspace{14mu} \ldots \mspace{14mu} 5999}}},} \\{{{Training}\mspace{14mu} {symbols}\mspace{14mu} {at}\mspace{14mu} {locations}\mspace{14mu} k} = {6000\mspace{14mu} \ldots \mspace{14mu} 6399}}\end{matrix}\quad$ p = mod(n, 4) XL_(k,,p)optionalN = 24000 k = mod[n +floor(n/6000), 6000]n = 0 . . . N − 1 $\begin{matrix}{{{rowA}(k)} = {{mod}\left( {{1 + {99 \cdot k} + {29 \cdot {{floor}\left( \frac{9 \cdot k}{25} \right)}} + {111 \cdot {{floor}\left( \frac{k}{400} \right)}}},256} \right)}} \\{{{{{colA}(k)} = {{mod}\left( {{9 \cdot k},25} \right)}};{\mspace{11mu} \;}{k = {0\mspace{14mu} \ldots \mspace{14mu} 5999}}},} \\{{{Training}\mspace{14mu} {symbols}\mspace{14mu} {at}\mspace{14mu} {locations}\mspace{14mu} k} = {6000\mspace{14mu} \ldots \mspace{14mu} 6399}}\end{matrix}\quad$ p = mod(n, 4)

The Interleaver Indices are: k=Modem Frame Symbol Index for MPAPartitions, or Block Symbol Index for IDS Partitions; and p=16-QAM codebit mapping within each 16-QAM symbol, (IMSB=0, ILSB=1, QMSB=2, QLSB=3),or QPSK code bit mapping within each QPSK symbol, (I=0, Q=1), whereI/Q=In phase/Quadrature, MSB or LSB of Gray-coded 4ASK symbols.

FIG. 5 is a block diagram of a radio receiver 150 constructed inaccordance with this invention. The DAB signal is received on antenna152. A bandpass preselect filter 154 passes the frequency band ofinterest, including the desired signal at frequency f_(c), but rejectsthe image signal at (f_(c)−2f_(if)), for a low side lobe injection localoscillator. Low noise amplifier 156 amplifies the signal. The amplifiedsignal is mixed in mixer 158 with a local oscillator signal f_(lo)supplied on line 160 by a tunable local oscillator 162. This creates sum(f_(c)+f_(lo)) and difference (f_(c)−f_(lo)) signals on line 164.Intermediate frequency filter 166 passes the intermediate frequencysignal f_(if) and attenuates frequencies outside of the bandwidth of themodulated signal of interest. An analog-to-digital converter 168operates using a clock signal f_(s) to produce digital samples on line170 at a rate f_(s). Digital down converter 172 frequency shifts,filters and decimates the signal to produce lower sample rate in-phaseand quadrature signals on lines 174 and 176. A digital signal processorbased demodulator 178 then provides additional signal processing toproduce an output signal on line 180 for output device 182.

A functional block diagram of the deinterleaver 190 and FEC decoderportions of a receiver are shown in FIGS. 6 and 7. The constellationdata at the input on line 192 includes the I and Q values for each ofthe QAM or QPSK symbols, which have been demodulated and normalized tothe constellation grid. Channel State Information (CSI) is associatedwith each I and Q value to permit subsequent soft-decision detection ofthe code bits. The Partitions AU, AL, B and C (and optionally XU and XL)are accumulated in an entire Modem Frame prior to deinterleaving, asshown in block 194. The deinterleaving and depuncturing are the reverseof operations performed in the transmitter. Block 196 shows that softdecision code bits are produced for the signals transmitted in thecentral ±20 kHz band and for the extended upper and lower sidebands ifused. The various partitions are deinterleaved as shown in blocks 198,200, 202, 204, 206 and 208. The deinterleaved bits for partitions AU,AL, B and C are delayed as shown in blocks 210, 212, 214 and 216. FECdecoding of the main program audio is then performed as shown in block218 to produce MPA packets on line 220.

FIG. 7 is a block diagram of the IDS decoding. The IDS signal is inputon line 222 and the assembled constellation data and channel stateinformation are assembled as shown in block 224. Soft decisions aregenerated as shown in block 226, which are subsequently deinterleaved asshown in block 228. The resulting IDSL and IDSU signals are then FECdecoded as illustrated by block 230 to produce IDS packets on line 232.The IDS functions are processed on interleaver Block boundaries (asopposed to Modem Frame boundaries) in order to minimize delay inprocessing the IDS data.

Since binary codes are used for CPTCM, it is necessary to obtain softbinary metrics from noisy M-ary symbols. Suppose that the received noisesymbol is:

y _(i) =s _(i) +n _(i) , i=1, . . . N.

Assuming K information bits per symbol, the binary metric for the k-thbit is given by:

${\lambda_{i,k} = {{\ln \; \frac{\Pr \left( {b_{k} = \left. 1 \middle| y_{i} \right.} \right)}{\Pr \left( {b_{k} = \left. 0 \middle| y_{i} \right.} \right)}} = {\ln \frac{\sum\limits_{{all}\mspace{14mu} s_{j}^{1,k}}{f_{n}\left( {y_{i} - s_{j}^{1,k}} \right)}}{\sum\limits_{{all}\mspace{14mu} s_{j}^{0,k}}{f_{n}\left( {y_{i} - s_{j}^{0,k}} \right)}}}}},{k = 1},\ldots \mspace{14mu},K$

where s_(j) ^(1,k) stands for the j-th symbol in the constellation thathas bit value 1 in the k-th bit position (and similarly for s_(j)^(0,k), the j-th symbol in the constellation that has bit value 0 in thek-th bit), and

${f_{n}(x)} = {\frac{1}{\sqrt{2{\pi\sigma}^{2}}}{\exp \left\lbrack {- \frac{x^{2}}{2\sigma^{2}}} \right\rbrack}}$

is the probability density function of noise, assuming AWG noise. Theabove formula for the soft bit metric applies for any constellation. Themain disadvantage of this approach is that it requires computations ofexponentials. An approximate metric can be obtained by approximating thesum of exponentials by the maximum exponential, so that:

$\begin{matrix}{{\lambda_{i,k} \cong {\ln \; \frac{\max_{{all}\mspace{11mu} s_{j}^{1,k}}{\exp \left\lbrack {{- \frac{1}{2\sigma_{i}^{2}}}\left( {y_{i} - s_{j}^{1,k}} \right)^{2}} \right\rbrack}}{\max_{{all}\mspace{11mu} s_{j}^{0,k}}{\exp \left\lbrack {{- \frac{1}{2\sigma_{i}^{2}}}\left( {y_{i} - s_{j}^{0,k}} \right)^{2}} \right\rbrack}}}},{k = 1},\ldots \mspace{14mu},K} \\{\cong {\frac{1}{\sigma_{i}^{2}}\left\lbrack {{y_{i}\left( {s_{\min}^{1,k} - s_{\min}^{0,k}} \right)} - {0.5\left( {s_{\min^{2}}^{1,k} - s_{\min^{2}}^{0,k}} \right)}} \right\rbrack}}\end{matrix}$

where irrelevant terms and constants are dropped and s^(1,k) _(min)denotes the symbol closest to y_(i) that has 1 in the k-th bit position(and similarly for s^(0,k) _(min)). Thus, by means of this approximation(the so called log-max approximation) the calculation of exponentials isavoided. However a fraction of dB can be lost in performance as aconsequence of using this approximation.

Next, consider possible improvements of soft metric for the impulsivenoise scenario. Assume that the noisy symbol sample is passed through anonlinearity in the form of a soft limiter or linear clipper. It isdesired to construct a soft metric that performs approximately the samein Average White Gaussian Noise (AWGN) as previously considered metrics,yet that will have smaller degradation in impulsive noise. That is, ithas to have enough “softness” to maximize the performance in AWGN and tolimit metric samples when impulsive noise is present, i.e. to preventthe excessive metric growth when large noise samples are present. FIGS.8 and 9 illustrate nonlinearities for 4-ASK and QPSK, respectively.

Based on the value of received noisy signal, soft metrics can beconstructed by passing the received sample through differentnonlinearities shown in FIGS. 8 and 9. The constructed soft bit valuesare further divided by the corresponding values of average noise powerestimated for the symbol. In summary, the soft metric can be representedby:

${soft\_ out}_{i} = \frac{F\left( y_{i} \right)}{\sigma_{i}^{2}}$

where y represents the received noisy symbol and F(.) is the desirednonlinearity from FIGS. 8 and 9.

The performance of surviving partitions under various interferencescenarios is set forth in Table 5.

TABLE 5 Performance of surviving partitions with interference HammingFree Distance error- PARTITIONS correcting (surviving) property ScenarioAL + AU + B + C + 12 All partitions (30 kHz) XL + XU (full 30 kHz optionFull time diversity XL + XU) No large interferers AL + AU + B + C + 8Eliminate XU XL (full 25 kHz optional XL) AL + AU + B + C + 8 EliminateXL XU (full 25 kHz optional XU) AL + AU + B + C 5 Main, (full 20 kHzoption) Or corrupted Backup XL, XU AL + AU + XL + XU 9 Co-channelInterferer B & C corrupted XL + XU 5 Backup time diverse, main corruptedAU + B + C + XU 6 Lower + center (B + C) AL, XL corrupted, ModerateLower First adjacent interferer AL + B + C + XL 6 Upper + center (B + C)AU, XU corrupted, Moderate Upper First adjacent interferer AU + B + XU 4Large Lower first adjacent interferer, or Lower second with XU AL + B +XL 3 Large Upper first adjacent interferer, or Upper second with XL AU +XU 1 Co-channel and Lower first and second adjacent interferers AL + XL1 Co-channel and Upper first and second adjacent interferers

The bits in the AU, AL, and the XU and XL partitions are truecomplementary pairs, whereas the B and C partitions are extra code bitsto improve coding gain. True complementary implies that one partition(e.g., AU) is a cyclic shift of the code bits of another partition(e.g., AL), and that these partitions (component codes) are goodnoncatastrophic codes by themselves having identical code properties.When the complementary partitions are combined, they form a code that isgenerally better than the sum of the two. In the method of thisinvention, the restriction that these codes be a cyclic shift of eachother with identical properties is not necessary.

This invention reduces adjacent channel interference relative to theprevious AM Hybrid system. It also introduces lower crosstalk to itsanalog AM host signal since the C partition spans about ±6 kHz at −50dBc/subcarrier, whereas previous design spans ±5 kHz and the 5 to 6 kHzrange is −43 dBc/subcarrier. In other words it is more compatible in theAM environment.

An important feature of this code is the flexibility of the design suchthat either of the optional XU or XL partitions can be eliminated orsuppressed to reduce adjacent channel interference. When one partitionis eliminated (e.g., XU), then the signal occupies approximately 25 kHz.When both are eliminated the BW is 20 kHz. This is an importantflexibility feature of the code to accommodate the adjacent channelassignments for a particular AM station. These features are preferredover creating new code designs for 20, 25 and 30 kHz options. Anotherfeature of this signal is that the outer partitions XU and XL (whenpresent) are reduced by 10 dB in power relative to the previous Hybriddesign. The B and C partitions are extra partitions in addition to thecomplementary partitions which provide additional coding gain in someinterference scenarios.

9 kHz or 10 kHz Channel-Spacing Systems

In another aspect, this invention provides a modified version of theCPTCM method of forward error correction (FEC) for application to the AMsignal. The method is based upon a combination of a new codepattern-mapping technique, and the application of ComplementaryPunctured Codes to an IBOC system, expanding the complementary-likeproperties to multiple dimensions. The coding and interleaving techniqueis designed to be flexible for operation with either 10 kHz or 9 kHzspaced channels in various regions around the world. Furthermore, theouter subcarriers may be reduced in power, or eliminated to mitigate theeffects of some interference scenarios.

The code bits to be transmitted are divided into five partitionsincluding a main upper (MU) partition, a main lower (ML) partition, abackup upper (BU) partition, a backup lower (BL) partition, and atertiary (T) partition. The addition of a fifth partition (i.e., thetertiary partition T) further improves robustness of the code. The fifthpartition (T) is an extra partition in addition to the original fouroverlapping partitions (MU, ML, BU, BL) as defined in the original CPTCMcode design description. This fifth partition provides additional errorcorrection code bits, improving robustness especially in the presence ofinterferers. The fifth partition does not overlap any of the otherpartitions, but can be combined with any of the other partitions in manyinterference scenarios to improve robustness.

This new mode carries audio in a single stream. The terms primary,secondary, and tertiary used in the following description identify thepartition regions. BU and BL identify the primary partitions, MU and MLidentify secondary partitions, and T identifies the newly definedtertiary partition.

A particular mode of operation is described below for a single stream(e.g., 24 kilobits per second (kbps)) of digital audio with reducedpower in the primary subcarriers (i.e., those subcarriers spaced 10 to15 kHz on either side from the main carrier).

A combination of reduced power and CPTCM coding with the additional codepartition is designed to reduce interference with minimal loss ofdigital coverage.

FIG. 10 is a schematic representation of the subcarrier assignments foran AM hybrid in-band on-channel digital audio broadcasting signalcompatible with 9 kHz channel spacing. FIG. 10 shows the subcarrierassignments in a channel 270 that encompasses a center frequency band272, an upper sideband 274, and a lower sideband 276. A main carrier 278is positioned at the center of the channel, and analog amplitudemodulated to produce an analog modulated signal 280 in the centerfrequency band. A plurality of subcarriers are positioned in the channelat evenly spaced frequencies. The positions of the subcarriers atfrequencies above the center frequency are designated as subcarrierpositions +1 through +78 (or optionally +1 through +73 for the 9 kHzchannel spacing mode). The positions of the subcarriers at frequenciesbelow the center frequency are designated as subcarrier positions −1through −78 (or optionally −1 through −73). The subcarriers at positions+1 and −1 are BPSK modulated timing subcarriers. The subcarriers atpositions +27, +53, −27 and −53 are used to transmit IDS information.

The remaining subcarriers are grouped into partitions including: primaryor main upper subcarriers 282 at positions +28 through +52; primary ormain lower subcarriers 284 at positions −28 through −52; secondary orbackup upper subcarriers 286 at positions +54 through +78 (or optionally+54 through +73); secondary or backup lower subcarriers 288 at positions−54 through −78 (or optionally −54 through −73); upper tertiarysubcarriers 290 at positions +2 through +26; lower tertiary subcarriers292 at positions −2 through −26.

In one embodiment for the 9 kHz channel spacing mode, the power spectraldensity of each subcarrier in the main upper (subcarriers 28 through 52)and main lower sidebands (subcarriers −28 through −52) is at least 40dBc below the power spectral density of the main carrier. The powerspectral density of each subcarrier in the backup upper (subcarriers 54through 78 (or 73)) and backup lower sidebands (subcarriers −54 through−78 (or 73)) is at least 40 dBc below the power spectral density of themain carrier. The power spectral density of each subcarrier located atpositions 2 through 26 and −2 through −26 is at least 50 dBc below thepower spectral density of the main carrier. The subcarriers at positions+1 and −1 are BPSK timing subcarriers. The subcarriers at positions +27,+53, −27 and −53 are used to transmit IDS information.

FIG. 11 is a schematic representation of the subcarrier assignments foran AM hybrid in-band on-channel digital audio broadcasting signalcompatible with 10 kHz channel spacing. This 10 kHz channel spacing modediffers from the 9 kHz channel spacing mode in the location of thebackup outer partitions. This 10 kHz channel spacing mode shifts theseouter backup partitions by 3 subcarrier locations (relative to the 9 kHzmode) to better accommodate main carrier interference with a 10 kHzfirst adjacent interferer. FIG. 11 shows the subcarrier assignments in achannel 300 that encompasses a center frequency band 302, an uppersideband 304, and a lower sideband 306. A main carrier 308 is positionedat the center of the channel, and analog amplitude modulated to producean analog modulated signal 310 in the center frequency band. A pluralityof subcarriers are positioned in the channel at evenly spacedfrequencies. The positions of the subcarriers at frequencies above thecenter frequency are designated as subcarrier positions +1 through +81.The positions of the subcarriers at frequencies below the centerfrequency are designated as subcarrier positions −1 through −81. Thesubcarriers at positions +1 and −1 are BPSK timing subcarriers. Thesubcarriers at positions +27, +53, −27 and −53 are used to transmit IDSinformation.

The remaining subcarriers are grouped into: primary or main uppersubcarriers 312 at positions +28 through +52; primary or main lowersubcarriers 314 at positions −28 through −52; secondary or backup uppersubcarriers 316 at positions +54 through +81; secondary or backup lowersubcarriers 318 at positions −54 through −81; upper tertiary subcarriers320 at positions +2 through +26; lower tertiary subcarriers 322 atpositions −2 through −26.

In one embodiment, the power spectral density of each subcarrier in theupper and lower sidebands is at least 40 dBc below the power spectraldensity of the main carrier. The power spectral density of eachsubcarrier located at positions 2 through 26 and −2 through −26 is atleast 50 dBc below the power spectral density of the main carrier.

Digital information is transmitted on the primary and secondary (mainand backup) subcarriers using quadrature amplitude modulation (QAM), andon the tertiary subcarriers using quadrature phase shift keying (QPSK).The digital information is forward error corrected and interleaved priorto modulation. The interleaving, FEC coding, and modulation aspects ofthe invention are described below. A comparison of the relativeperformance of a signal broadcast in accordance with an aspect of theinvention with respect to a prior hybrid mode is presented below.

The CPTCM technique is applied to a QAM symbol by treating the I and Qcomponents as independently coded and modulated ASK signals.Specifically, a 16-QAM symbol is created by modulating the I and Qcomponents with independent 4-ASK signals. The 4-ASK symbols aregenerated from specially selected 2-bit groups which are then used toaddress the Gray-mapped constellation points. In one example, themapping of the code-bit pairs to the four levels of the 4-ASK symbols ispresented in Table 6.

TABLE 6 Mapping of CPTCM-coded bits to four levels of the 4-ASK symbols.Level Level Level Level MAPPING −1.5 −0.5 +0.5 +1.5 A = MSB 0 0 1 1 B =LSB 0 1 1 0

The interleaver in one example is designed for CPTCM with a nominal 24kbps single stream audio codec. The interleaver is comprised of 6 groupsof 25 subcarriers each. The 6 groups include the primary, secondary, andtertiary groups, each having an upper and lower partition as shown inFIGS. 10 and 11. All subcarriers in the primary and secondary groups aremodulated with 16-QAM symbols. The code bits that modulate the symbolsare defined in the interleaver description below.

The tertiary subcarriers are modulated with QPSK symbols. The upper andlower tertiary groups are described as complementary, meaning that thelower tertiary group is modulated with the same code bits as the mirrorimage (negative complex conjugate) of the upper tertiary group. Twoadditional subcarrier pairs (at subcarrier locations ±27 and ±53) areused for integrated digital services (IDS) information, and are codedseparately. The analog AM signal must be limited to less than ±5 kHzsince the secondary partitions are not complementary.

The CPTCM code can be created through puncturing and partitioning of arate-⅓ convolutional FEC code. The FEC code requires appropriatepuncture patterns and code-bit mapping to provide good results. Thepuncture pattern assigns code bits to the groups of subcarrierpartitions. The combined puncture patterns for the partitions of the FECcode for one example are defined in Tables 7 and 8. Table 7 shows thepuncture pattern bit mapping to the main (M), backup (B), and tertiary(T) partitions. The main and backup partitions are further separatedinto A and B groups representing the most significant bit (MSB) andleast significant bit (LSB) Gray-code mapping, respectively, in each Ior Q 16-QAM symbol dimension. The tertiary partition uses conventionalQPSK, so there are I and Q bits, but no A or B designation. For example,the bit ordering for the first 4 bits (n=0 . . . 3) of the MUinterleaver would be MU_(IA), MU_(IB), MU_(QA), and MU_(QB). Theordering and interleaver details are further described below.

TABLE 7 Puncture Pattern code bit assignments for R = 1/3 FEC code, withG = [G1 = 561o, G2 = 657o, G3 = 711o]. Data Data Data Data Data Data bit0 bit 1 bit 2 bit 3 bit 4 bit 5 G1 BU_(IB) MU_(IA) ML_(IA) BU_(QB)MU_(QA) ML_(QA) G2 BL_(IB) T_(I) MU_(IB) BL_(QB) T_(Q) MU_(QB) G3ML_(IB) BL_(IA) BU_(IA) ML_(QB) BL_(QA) BU_(QA)

TABLE 8 Performance metrics for code partitions, including rate, Hammingdistance d_(free), and number of paths (a). Metric COMP M + T B + T M BL + T U + T L U Rate 1/3 3/5 3/5 3/4 3/4 3/5 3/5 3/4 3/4 d_(free) 17 8 76 5 7 6 5 5 a 12 10 1 15 1 3 1 2 2

The number of paths (a) represents the number of paths through theconvolutional coding trellis that are at a Hamming distance d_(free)away from the correct path. Punctured codes with larger d_(free) valueshave better performance than smaller values of d_(free), while puncturedcodes with the same d_(free) value are better with a smaller number ofpaths (a).

The IDS subcarriers are modulated using 16-QAM symbols. Subcarriers atlocations 27, 53, −27 and −53 are IDS subcarriers in the hybrid system.Subcarriers at locations −27 and −53 are complementary to thesubcarriers at locations 27 and 53. In one example, the IDS sequence is32 symbols long (symbols 0 through 31) and associated with a blocklength. Symbol locations 10 and 26 are assigned training symbols. Theremaining 30 symbols carry 120 bits of rate-⅔ coded information. Hence,each IDS sequence carries 80 information bits, including an 8-bit cyclicredundancy check (CRC). A rate-⅓ code is employed with rate-⅔complementary components. The upper and lower complementary codecomponents of the all-digital IDS subcarriers correspond to the hybridinner and outer IDS complementary subcarrier pairs, respectively.

TABLE 9 Puncture pattern bit assignments for IDS, with G = [G1 = 561o,G2 = 753o, G3 = 711o]. Data bit 0 Data bit 1 Data bit 2 Data bit 3 Databit 4 Data bit 5 Data bit 6 Data bit 7 G1 IDSL_(IA0) IDSU_(IA1)IDSL_(IA1) IDSU_(IA2) IDSL_(QA0) IDSU_(QA1) IDSL_(QA1) IDSU_(QA2) G2IDSL_(IB0) IDSU_(IB0) IDSL_(IB2) IDSU_(IB2) IDSL_(QB0) IDSU_(QB0)IDSL_(QB2) IDSU_(QB2) G3 IDSU_(IA0) IDSL_(IB1) IDSU_(IB1) IDSL_(IA2)IDSU_(QA0) IDSL_(QB1) IDSU_(QB1) IDSL_(QA2)

TABLE 10 IDS FEC summary of parameters. Metric COMP Upper Lower Rate 1/32/3 2/3 dfree 17 7 7 a 3 3 3

In one example, the interleaver blocks consist of 32 COFDM symbols(bauds). There are 8 blocks in a modem frame. The backup partition isinterleaved over only 1 block span to permit rapid digital tuning. Eachblock holds a total of 800 QAM symbols (750 data +50 training).

Interleaving within each block spanning 25 subcarriers and 32 OFDMsymbols is performed using the following expressions for the row andcolumn indices:

${{row}(k)} = {{mod}\begin{bmatrix}{{11 \cdot {{mod}\left( {{9 \cdot k},25} \right)}} +} \\{{{{16 \cdot {floor}}\left( \frac{k}{25} \right)} + {11 \cdot {{floor}\left( \frac{k}{50} \right)}}},32}\end{bmatrix}}$ col(k) = mod[9 ⋅ k, 25] k = 0  …  749.

The index k points to one of the 750 QAM symbols within the block. Eachof the 16-QAM symbols carries 4 code bits, which are mapped to the 16QAM constellation within a block. Of the total of 800 symbols in ablock, the remaining 50 QAM symbols are used for training symbols. Thetraining symbols are located in the last 50 QAM symbol locations. Therow and columns are indexed using the last 50 values of k. In thisexample, the training symbol locations are: k 750 . . . 799.

TABLE 11 Symbol indices within a Block, with Training Symbol = “T”. 0 12 3 4 5 6 7 8 9 10 11 12 A = 0 0 “T” 728 692 631 595 534 498 437 376 340279 243 1 150 114 53 17 “T” 745 684 648 587 526 490 429 393 2 300 264203 167 106 70 9 “T” 737 676 640 579 543 3 450 414 353 317 256 220 159123 62 1 “T” 729 693 4 600 564 503 467 406 370 309 273 212 151 115 54 185 “T” 714 653 617 556 520 459 423 362 301 265 204 168 6 125 89 28 “T”706 670 609 573 512 451 415 354 318 7 275 239 178 142 81 45 “T” 723 662601 565 504 468 8 425 389 328 292 231 195 134 98 37 “T” 715 654 618 9575 539 478 442 381 345 284 248 187 126 90 29 “T” 10 725 689 628 592 531495 434 398 337 276 240 179 143 11 50 14 “T” 742 681 645 584 548 487 426390 329 293 12 200 164 103 67 6 “T” 734 698 637 576 540 479 443 13 350314 253 217 156 120 59 23 “T” 726 690 629 593 14 500 464 403 367 306 270209 173 112 51 15 “T” 743 15 650 614 553 517 456 420 359 323 262 201 165104 68 16 25 “T” 703 667 606 570 509 473 412 351 315 254 218 17 175 13978 42 “T” 720 659 623 562 501 465 404 368 18 325 289 228 192 131 95 34“T” 712 651 615 554 518 19 475 439 378 342 281 245 184 148 87 26 “T” 704668 20 625 589 528 492 431 395 334 298 237 176 140 79 43 21 “T” 739 678642 581 545 484 448 387 326 290 229 193 22 100 64 3 “T” 731 695 634 598537 476 440 379 343 23 250 214 153 117 56 20 “T” 748 687 626 590 529 49324 400 364 303 267 206 170 109 73 12 “T” 740 679 643 25 550 514 453 417356 320 259 223 162 101 65 4 “T” 26 700 664 603 567 506 470 409 373 312251 215 154 118 27 75 39 “T” 717 656 620 559 523 462 401 365 304 268 28225 189 128 92 31 “T” 709 673 612 551 515 454 418 29 375 339 278 242 181145 84 48 “T” 701 665 604 568 30 525 489 428 392 331 295 234 198 137 7640 “T” 718 31 675 639 578 542 481 445 384 348 287 226 190 129 93 13 1415 16 17 18 19 20 21 22 23 24 A = 0 182 146 85 49 “T” 702 666 605 569508 472 411 1 332 296 235 199 138 77 41 “T” 719 658 622 561 2 482 446385 349 288 227 191 130 94 33 “T” 711 3 632 596 535 499 438 377 341 280244 183 147 86 4 “T” 746 685 649 588 527 491 430 394 333 297 236 5 10771 10 “T” 738 677 641 580 544 483 447 386 6 257 221 160 124 63 2 “T” 730694 633 597 536 7 407 371 310 274 213 152 116 55 19 “T” 747 686 8 557521 460 424 363 302 266 205 169 108 72 11 9 707 671 610 574 513 452 416355 319 258 222 161 10 82 46 “T” 724 663 602 566 505 469 408 372 311 11232 196 135 99 38 “T” 716 655 619 558 522 461 12 382 346 285 249 188 12791 30 “T” 708 672 611 13 532 496 435 399 338 277 241 180 144 83 47 “T”14 682 646 585 549 488 427 391 330 294 233 197 136 15 7 “T” 735 699 638577 541 480 444 383 347 286 16 157 121 60 24 “T” 727 691 630 594 533 497436 17 307 271 210 174 113 52 16 “T” 744 683 647 586 18 457 421 360 324263 202 166 105 69 8 “T” 736 19 607 571 510 474 413 352 316 255 219 158122 61 20 “T” 721 660 624 563 502 466 405 369 308 272 211 21 132 96 35“T” 713 652 616 555 519 458 422 361 22 282 246 185 149 88 27 “T” 705 669608 572 511 23 432 396 335 299 238 177 141 80 44 “T” 722 661 24 582 546485 449 388 327 291 230 194 133 97 36 25 732 696 635 599 538 477 441 380344 283 247 186 26 57 21 “T” 749 688 627 591 530 494 433 397 336 27 207171 110 74 13 “T” 741 680 644 583 547 486 28 357 321 260 224 163 102 665 “T” 733 697 636 29 507 471 410 374 313 252 216 155 119 58 22 “T” 30657 621 560 524 463 402 366 305 269 208 172 111 31 32 “T” 710 674 613552 516 455 419 358 322 261

FIGS. 12 and 13 illustrate the mapping of coded bits to interleaverpartitions and blocks. In the illustrated example, 36000 informationbits comprising each modem frame are coded and assembled in groups ofbits from the puncture patterns described above. These groupings aremapped into the interleaver using the expressions presented Table 12.

FIG. 12 is a functional block diagram illustrating a forward errorcorrection (FEC) interleaver 330 for a nominal 24-kbps single stream AMIBOC system. A digital signal is supplied on line 332 and assembled intoa modem frame containing, for example, 3600 bits, as illustrated byblock 334. The modem frame is then divided into a plurality of bitgroups as illustrated by block 336, wherein the modem frame is shown tobe divided into 6000 6-bit groups. The groups are then subjected toforward error encoding, puncturing, and partitioning as illustrated byblock 338 to produce 8-bit outputs.

In the example illustrated in FIG. 12, each of the 6-bit groups resultsin a 18-bit output. The 18-bit groups are partitioned into main-upper,main-lower, tertiary, backup-upper and backup-lower partitions asillustrated by blocks 340, 342, 344, 346 and 348, for example byallocating four bits of each 18-bit group to each of the main upper,main lower, backup upper and backup lower partitions, and 2 bits to thetertiary partition. The tertiary, backup upper and backup lower bits aredelayed by three modem frames as illustrated by blocks 350, 352 and 354to create time diversity, and the bits are mapped into the interleaveras shown by block 356.

The interleaver indices in this example are: k=block symbol index, 0 to749 symbols in each block; b=block number, 0 to 7 within each modemframe; and p=16-QAM bit mapping within each 16-QAM symbol, (IA=0, IB=1,QA=2, QB=3) or QPSK bit mapping within each QPSK symbol, (I=0, Q=1),where I=in-phase, Q=quadrature, and 16 QAM is Gray-coded with MSB & LSBin each I or Q.

TABLE 12 Interleaver Mapping Partition N, n = k b p X_(k, b, p) 0 . . .N − 1 index in block b block # I&Q mapping MU_(k, b, p) 24000 mod[n +floor(n/6000), mod[3*n + floor(n/3000) + mod(n, 4) 750]2*floor(n/12000), 8] ML_(k, b, p) 24000 mod[n + floor(n/6000) +mod[3*n + floor(n/3000) + mod(n, 4) 1, 750] 2*floor(n/12000) + 3, 8]T_(k, b, p) 12000 mod[n + floor(n/750), floor(n/1500) (see note 1)mod(n, 2) QPSK 750] BU_(k, b, p) 24000 mod[n + floor(n/1500),floor(n/3000) (see note 1) mod(n, 4) 750] BL_(k, b, p) 24000 mod[n +floor(n/1500) + floor(n/3000) (see note 1) mod(n, 4) 1, 750]

To map the IDS coded bits to interleaver partitions and blocks, the 80IDS information bits comprising each block can be coded and assembled ingroups of bits from the puncture patterns, as illustrated in FIG. 13.FIG. 13 shows the functionality of an FEC interleaver for the IDSchannel. A digital signal is supplied on line 360 and assembled into amodem frame core containing, for example, 80 bits, as illustrated byblock 362. The modem frame is then divided into a plurality of bitgroups as illustrated by block 364, wherein the modem frame is shown tobe divided into ten 8-bit groups. The groups are then subjected toforward error encoding and puncturing as illustrated by block 366. Inthis example, each of the 8-bit groups results in a 24-bit output. The24-bit groups are then partitioned into IDS upper and IDS lowerpartitions as illustrated by blocks 368 and 370, for example byallocating six bits of each 12-bit group to each of the partitions. TheIDS upper and IDS lower bits are then mapped into an enhancementinterleaver as shown by block 372.

In this example, these groupings are mapped into the IDS interleaverusing the expressions presented in Table 13. The IDS interleaver indicesin this example are: k=block index, 0 to 29 symbols in each block,skipping the two training symbols (8 and 24) of 32 total; and p=16-QAMbit mapping within each 16-QAM symbol, (IA=0, IB=1, QA=2, QB=3).

TABLE 13 IDS Interleaver Mapping. k p Partition N index in I&Q, ASKX_(k, p) n = 0 . . . N − 1 IDS sequence mapping IDSU_(k, p) 120 mod(n +mod(n, 4) floor(n/60), 30) IDSL_(k, p) 120 mod(n + mod(n, 4)floor(n/60) + 11, 30)

Interleaving within each IDS sequence spanning 32 OFDM symbols can beperformed using the following expression for the row (vector) index:

${{row}(k)} = {{mod}\left\lbrack {11 \cdot \left( {{k + {{floor}\left( \frac{k}{15} \right)} + 3},32} \right)} \right\rbrack}$k = 0  …  29 ${{IDS\_ interleaver} = \begin{matrix}\; & 0 \\0 & 22 \\1 & 25 \\2 & 28 \\3 & 0 \\4 & 3 \\5 & 6 \\6 & 9 \\7 & 12 \\8 & {{}_{}^{}{}_{}^{}} \\9 & 17 \\10 & 20 \\11 & 23 \\12 & 26 \\13 & 29 \\14 & 1 \\15 & 4 \\16 & 7 \\17 & 10 \\18 & 13 \\19 & 15 \\20 & 18 \\21 & 21 \\22 & 24 \\23 & 27 \\24 & {{}_{}^{}{}_{}^{}} \\25 & 2 \\26 & 5 \\27 & 8 \\28 & 11 \\29 & 14 \\30 & 16 \\31 & 19\end{matrix}}$

The index k points to one of the 32 16-QAM symbols within the IDSsequence. Each of the 16-QAM symbols carries 4 code bits. Of the totalof 32 symbols, 30 carry IDS information while the remaining 2 symbolsare used for training symbols (locations 8 and 24).

FIG. 14 is a simplified functional block diagram of an AM IBOC DABreceiver 400, which can receive signals coded in accordance with themethod of the present invention. The receiver includes an input 402connected to an antenna 404, a tuner or front end 406, and a digitaldown converter 408 for producing a baseband signal on line 410. Ananalog demodulator 412 demodulates the analog modulated portion of thebaseband signal to produce an analog audio signal on line 414. A digitaldemodulator 416 demodulates the digitally modulated portion of thebaseband signal. Then the digital signal is deinterleaved by adeinterleaver 418, and decoded by a Viterbi decoder 420. A servicedemodulator 422 separates main and supplemental program signals fromdata signals. A processor 424 processes the program signals to produce adigital audio signal on line 426. The analog and main digital audiosignals are blended as shown in block 428, or a supplemental digitalaudio signal is passed through, to produce an audio output on line 430.A data processor 432 processes the data signals and produces data outputsignals on lines 434, 436 and 438. The data signals can include, forexample, a station information service (SIS), main program service data(MPSD), supplemental program service data (SPSD), and one or moreauxiliary application services (AAS).

Functional block diagrams of the deinterleaver and FEC decoder portionsof a receiver are shown in FIGS. 15 and 16. FIG. 15 is a functionalblock diagram of a hybrid deinterleaver and FEC decoder implementationthat permits rapid acquisition of audio. The interleaved and forwarderror corrected symbols are received as an input on line 450 andsubjected to constellation bit branch metrics including channel stateinformation, as illustrated in block 452.

Unlike the transmitter that modulates code bits, the receiver must dealwith noisy estimates of these code bits. These noisy estimates areprocessed in the receiver as branch metrics and channel stateinformation (CSI) which are subsequently used by the convolutional(Viterbi) decoder to convert this noisy stream of branch metrics,weighted by CSI, into the original information bit sequence.

Block 454 shows that the branch metrics are partitioned into main upperand main lower partitions on lines 456 and 458. The partitioning is akey aspect of the CPTCM code design. Different partitions may beaffected, or corrupted, by different interferers. Grouping the code bitsinto these partitions results in less performance loss than if thesecode bits were not partitioned. This is accomplished by ensuring good(punctured) FEC codes in the surviving partitions.

The main upper and main lower partitions are deinterleaved as shown inblocks 460 and 462 and delayed as illustrated by blocks 464 and 466.Then the delayed and the deinterleaved forward error corrected mainupper and main lower signals are decoded as illustrated by block 268 toproduce decoded bits on line 470.

Block 472 shows that the branch metrics are also partitioned into atertiary partition on line 474. The tertiary partition is deinterleavedas shown in blocks 476. The deinterleaved tertiary signals are decodedas illustrated by block 478 to produce decoded bits on line 470.

Block 480 shows that the branch metrics are also partitioned into backupupper and backup lower partitions on lines 482 and 484. Then thedeinterleaved forward error corrected backup upper and backup lowersignals are deinterleaved as shown in blocks 486 and 488, and decoded asillustrated by block 490 to produce decoded bits on line 470.

FIG. 16 is a functional block diagram of the IDS deinterleaver and FECdecoder. The interleaved and forward error corrected IDS signal is inputon line 500, and arranged in 80-bit groups as shown in block 502. Block504 shows that soft decisions for the I and Q components are determined,and the I and Q soft decisions are deinterleaved in block 506. Thedeinterleaved forward error corrected IDS signals are decoded asillustrated by block 508 to produce the IDS data on line 510.

The constellation data at the input includes the I and Q values for eachof the QAM symbols, which have been demodulated and normalized to theconstellation grid. Channel state information (CSI) is associated witheach I and Q value to permit subsequent soft-decision detection of thebits. The purpose of the delay elements in FIG. 15 is to time-align themain (MU and ML) audio information with the BU, BL and T audioinformation, which has already been delayed at the transmitter. The MUand ML blocks of bits are accumulated in an entire L1 modem frame priorto deinterleaving. The BU and BL are deinterleaved in blocks. Boxes 452,472, 476, 480, 486, 488 and 490 in FIG. 15 indicate functions that mustbe processed on interleaver block boundaries (as opposed to L1 modemframe boundaries) in order to minimize delay in processing the backup orIDS data.

Since binary codes are used for CPTCM, it is necessary to obtain softbinary metrics from noisy M-ary symbols. The soft binary metrics can beobtained as described above for the 20 kHz or 30 kHz system.

The performance of a 24-kbps single stream can be compared to the 20kbps core performance of the AM Hybrid MA1 codes described above for the20 kHz and 30 kHz system. The most significant changes with the 24-kbpssingle stream system are in the symbol modulation, power levels, FECcoding, and the addition of a fifth, non-overlapping partition (T).Using the spectral allocations of FIG. 10, 16-QAM modulation can beimplemented over the 100 primary and secondary subcarriers. The fifthQPSK partition (T) is employed in the tertiary region.

The power levels of the subcarriers are reduced to mitigateinterference. Specifically the outer primary subcarriers are reduced byat least 10 dB relative to the previously known MA1 mode. Since thesingle stream is carried over all partitions, 3 dB is gained, making thepower loss only 7 dB. Furthermore, the tertiary region power recoversthe equivalent of 0.8 dB of the power loss in the composite code;however an extra 0.8 dB (coincidentally) is needed to carry 24 kbps overthe 20 kbps current system.

The plots in FIGS. 17 and 18 illustrate a reduction in power andincrease in throughput over a previously known system. FIG. 17 showsAWGN performance of all the partitions (Composite) as shown by line 530,compared to previously known core 532 and enhanced 534 coverage in apreviously existing system. FIG. 18 shows AWGN performance of all thepartitions (Composite) as shown by line 536, compared to previouslyknown core 538 and enhanced 540 coverage in the presence of a strongsecond adjacent hybrid interferer.

The plot of FIG. 17 shows the performance of the previously known hybridsystem compared to a single stream system implementation of thisinvention, after adjustments for power loss and bit rates. The resultsshow that the single stream mode experiences approximately a 4.5 dB lossrelative to the previous MA1 system in AWGN for core coverage. Incomparison the MA1 Enhancement loses about 9 dB. In strong secondadjacent interference, the relative loss is less than 1 dB, as shown inFIG. 18. However, the effect of the interference on the analog signal isreduced by 10 dB. The analog interference and mutual digitalinterference can be further reduced by reducing the power on theinterfering primary partition. This would also benefit the performancefor digital-to-digital interference. Furthermore, the 9 kHz mode in areal environment experiences lower tracking and equalization losses dueto 16-QAM vs. 64 QAM. These performance scenarios can be quantified inactual testing.

In one aspect, this invention provides a 9 kHz mode for operation inregions where AM channels are spaced by a minimum of 9 kHz (not 10 kHz).The outer partition was moved in by 3 subcarriers (closing the nullsubcarriers around +10 kHz). The 5 outer primary subcarriers areoptional, further reducing the signal bandwidth for third adjacentinterference compatibility.

The tertiary partition improves robustness in interference, and offsetsthe loss due to the reduction in outer primary partition power, which isreduced by 10 dB relative to the previous design. Furthermore, the outerprimary partition modulation was changed from 64 QAM to 16 QAM, whichreduces the Signal-to-Noise (SNR) requirement for detection by 6 dB. Theremaining 4 dB (10 dB −6 dB) is offset by the tertiary partition.

The outer primary partition power has been reduced by at least 10 dB toreduce first and second adjacent channel interference, while increasingthe single stream throughput to 24 kbps.

While the present invention has been described in terms of particularembodiments, it will be apparent to those skilled in the art thatvarious changes can be made to the disclosed embodiments withoutdeparting from the scope of the invention as set forth in the followingclaims.

1. A method of broadcasting an AM compatible digital audio broadcastingsignal, the method comprising: producing an analog modulated carriersignal centrally positioned in a radio channel, wherein the analogmodulated carrier signal is modulated by an analog signal; producing aplurality of digitally modulated subcarrier signals in the radiochannel, wherein the digitally modulated subcarrier signals aremodulated using complementary pattern-mapped trellis code modulation(CPTCM) including a code mapped to overlapping partitions including anupper main partition, a lower main partition, an upper backup partitionand a lower backup partition, and a non-overlapping tertiary partition;and transmitting the analog modulated carrier signal and the pluralityof digitally modulated subcarrier signals.
 2. The method of claim 1,wherein the code forms a single stream audio signal.
 3. The method ofclaim 2, wherein the subcarrier signals in the upper backup partitionand the lower backup partition are modulated using 16-QAM.
 4. The methodof claim 1, wherein the subcarriers include upper main subcarriers,lower main subcarriers, upper backup subcarriers, lower backupsubcarriers, and tertiary subcarriers, with the power spectral densityof each of the upper main subcarriers, lower main subcarriers, upperbackup subcarriers, lower backup subcarriers, being at least 40 dBcbelow the power spectral density of an analog modulated carrier in thesame channel as the subcarriers, and the power spectral density of eachof the tertiary subcarriers, being at least 50 dBc below the powerspectral density of the analog modulated carrier.
 5. The method of claim4, wherein the subcarriers further include timing subcarriers andintegrated digital service subcarriers; and each of the subcarriers islocated at one of a plurality of evenly spaced frequency locations, withthe timing subcarriers being at locations +1 and −1, the upper tertiarysubcarriers being at locations +2 through +26, the lower tertiarysubcarriers being at locations −2 through −26, the upper mainsubcarriers being at locations +28 through +52, the lower mainsubcarriers being at locations −28 through −52, the upper backupsubcarriers being at locations +54 through +78, the lower backupsubcarriers being at locations −54 through −78, and the integrateddigital service subcarriers being at locations +27, +53, −27 and −53. 6.The method of claim 4, wherein the subcarriers further include timingsubcarriers and integrated digital service subcarriers; and each of thesubcarriers is located at one of a plurality of evenly spaced frequencylocations, with the timing subcarriers being at locations +1 and −1, theupper tertiary subcarriers being at locations +2 through +26, the lowertertiary subcarriers being at locations −2 through −26, the upper mainsubcarriers being at locations +28 through +52, the lower mainsubcarriers being at locations −28 through −52, the upper backupsubcarriers being at locations +54 through +73, the lower backupsubcarriers being at locations −54 through −73, and the integrateddigital service subcarriers being at locations +27, +53, −27 and −53. 7.The method of claim 4, wherein the subcarriers further include timingsubcarriers and integrated digital service subcarriers; and each of thesubcarriers is located at one of a plurality of evenly spaced frequencylocations, with the timing subcarriers being at locations +1 and −1, theupper tertiary subcarriers being at locations +2 through +26, the lowertertiary subcarriers being at locations −2 through −26, the upper mainsubcarriers being at locations +28 through +52, the lower mainsubcarriers being at locations −28 through −52, the upper backupsubcarriers being at locations +57 through +81, the lower backupsubcarriers being at locations −57 through −81, and the integrateddigital service subcarriers being at locations +27, +53, −27 and −53. 8.A transmitter for broadcasting an AM compatible digital audiobroadcasting signal, the transmitter comprising: a processor formodulating a plurality of subcarriers using complementary pattern-mappedtrellis code modulation (CPTCM) including a code mapped to overlappingpartitions including an upper main partition, a lower main partition, anupper backup partition and a lower backup partition, and anon-overlapping tertiary partition; and a transmitter for transmittingan analog modulated carrier signal and the plurality of digitallymodulated subcarrier signals.
 9. The transmitter of claim 8, wherein thecode forms a single stream audio signal.
 10. The transmitter of claim 8,wherein the subcarrier signals in the upper backup partition and thelower backup partition are modulated using 16-QAM.
 11. The transmitterof claim 8, wherein the subcarriers include upper main subcarriers,lower main subcarriers, upper backup subcarriers, lower backupsubcarriers, and tertiary subcarriers, with the power spectral densityof each of the upper main subcarriers, lower main subcarriers, upperbackup subcarriers, lower backup subcarriers, being at least 40 dBcbelow the power spectral density of an analog modulated carrier in thesame channel as the subcarriers, and the power spectral density of eachof the tertiary subcarriers, being at least 50 dBc below the powerspectral density of the analog modulated carrier.
 12. The transmitter ofclaim 11, wherein the subcarriers further include timing subcarriers andintegrated digital service subcarriers; and each of the subcarriers islocated at one of a plurality of evenly spaced frequency locations, withthe timing subearriers being at locations +1 and −1, the upper tertiarysubcarriers being at locations +2 through +26, the lower tertiarysubcarriers being at locations −2 through −26, the upper mainsubcarriers being at locations +28 through +52, the lower mainsubcarriers being at locations −28 through −52, the upper backupsubcarriers being at locations +54 through +78, the lower backupsubcarriers being at locations −54 through −78, and the integrateddigital service subcarriers being at locations +27, +53, −27 and −53.13. The transmitter of claim 11, wherein the subcarriers further includetiming subcarriers and integrated digital service subcarriers; and eachof the subcarriers is located at one of a plurality of evenly spacedfrequency locations, with the timing subcarriers being at locations +1and −1, the upper tertiary subcarriers being at locations +2 through+26, the lower tertiary subcarriers being at locations −2 through −26,the upper main subcarriers being at locations +28 through +52, the lowermain subcarriers being at locations −28 through −52, the upper backupsubcarriers being at locations +54 through +73, the lower backupsubcarriers being at locations −54 through −73, and the integrateddigital service subcarriers being at locations +27, +53, −27 and −53.14. The transmitter of claim 11, wherein the subcarriers further includetiming subcarriers and integrated digital service subcarriers; and eachof the subcarriers is located at one of a plurality of evenly spacedfrequency locations, with the timing subcarriers being at locations +1and −1, the upper tertiary subcarriers being at locations +2 through+26, the lower tertiary subcarriers being at locations −2 through −26,the upper main subcarriers being at locations +28 through +52, the lowermain subcarriers being at locations −28 through −52, the upper backupsubcarriers being at locations +57 through +81, the lower backupsubcarriers being at locations −57 through −81, and the integrateddigital service subcarriers being at locations +27, +53, −27 and −53.15. A method of receiving an AM compatible digital audio broadcastingsignal, the method comprising: receiving an analog modulated carriersignal centrally positioned in a radio channel, and a plurality ofdigitally modulated subcarrier signals in the radio channel, wherein thedigitally modulated subcarrier signals are modulated using complementarypattern-mapped trellis code modulation (CPTCM) including a code mappedto overlapping partitions including an upper main partition, a lowermain partition, an upper backup partition and a lower backup partition,and a non-overlapping tertiary partition; and demodulating the analogmodulated carrier signal and the plurality of digitally modulatedsubcarrier signals; and producing an output signal in response to thedemodulating step.
 16. The method of claim 15, wherein the code forms asingle stream audio signal.
 17. The method of claim 16, wherein thesubcarrier signals in the upper backup partition and the lower backuppartition are modulated using 16-QAM.
 18. The method of claim 15,wherein the subcarriers include upper main subcarriers, lower mainsubcarriers, upper backup subcarriers, lower backup subcarriers, andtertiary subcarriers, with the power spectral density of each of theupper main subcarriers, lower main subcarriers, upper backupsubcarriers, lower backup subcarriers, being at least 40 dBc below thepower spectral density of an analog modulated carrier in the samechannel as the subcarriers, and the power spectral density of each ofthe tertiary subcarriers, being at least 50 dBc below the power spectraldensity of the analog modulated carrier.
 19. The method of claim 18,wherein the subcarriers further include timing subcarriers andintegrated digital service subcarriers; and each of the subcarriers islocated at one of a plurality of evenly spaced frequency locations, withthe timing subcarriers being at locations +1 and −1, the upper tertiarysubcarriers being at locations +2 through +26, the lower tertiarysubcarriers being at locations −2 through −26, the upper mainsubcarriers being at locations +28 through +52, the lower mainsubcarriers being at locations −28 through −52, the upper backupsubcarriers being at locations +54 through +78, the lower backupsubcarriers being at locations −54 through −78, and the integrateddigital service subcarriers being at locations +27, +53, −27 and −53.20. The method of claim 18, wherein the subcarriers further includetiming subcarriers and integrated digital service subcarriers; and eachof the subcarriers is located at one of a plurality of evenly spacedfrequency locations, with the timing subcarriers being at locations +1and −1, the upper tertiary subcarriers being at locations +2 through+26, the lower tertiary subcarriers being at locations −2 through −26,the upper main subcarriers being at locations +28 through +52, the lowermain subcarriers being at locations −28 through −52, the upper backupsubcarriers being at locations +54 through +73, the lower backupsubcarriers being at locations −54 through −73, and the integrateddigital service subcarriers being at locations +27, +53, −27 and −53.21. The method of claim 18, wherein the subcarriers further includetiming subcarriers and integrated digital service subcarriers; and eachof the subcarriers is located at one of a plurality of evenly spacedfrequency locations, with the timing subcarriers being at locations +1and −1, the upper tertiary subcarriers being at locations +2 through+26, the lower tertiary subcarriers being at locations −2 through −26,the upper main subcarriers being at locations +28 through +52, the lowermain subcarriers being at locations −28 through −52, the upper backupsubcarriers being at locations +57 through +81, the lower backupsubcarriers being at locations −57 through −81, and the integrateddigital service subcarriers being at locations +27, +53, −27 and −53.22. A receiver receiving an AM compatible digital audio broadcastingsignal, the receiver comprising: an input for receiving an analogmodulated carrier signal centrally positioned in a radio channel, and aplurality of digitally modulated subcarrier signals in the radiochannel, wherein the digitally modulated subcarrier signals aremodulated using complementary pattern-mapped trellis code modulation(CPTCM) including a code mapped to overlapping partitions including anupper main partition, a lower main partition, an upper backup partitionand a lower backup partition, and a non-overlapping tertiary partition;a demodulator for demodulating the plurality of subcarriers with thepartitioned bits; and an output for producing an output signal inresponse to the demodulator.
 23. The receiver of claim 22, wherein thecode forms a single stream audio signal.
 24. The receiver of claim 23,wherein the subcarrier signals in the upper backup partition and thelower backup partition are modulated using 16-QAM.
 25. The receiver ofclaim 22, wherein the subcarriers include upper main subcarriers, lowermain subcarriers, upper backup subcarriers, lower backup subcarriers,and tertiary subcarriers, with the power spectral density of each of theupper main subcarriers, lower main subcarriers, upper backupsubcarriers, lower backup subcarriers, being at least 40 dBc below thepower spectral density of an analog modulated carrier in the samechannel as the subcarriers, and the power spectral density of each ofthe tertiary subcarriers, being at least 50 dBc below the power spectraldensity of the analog modulated carrier.
 26. The receiver of claim 25,wherein the subcarriers further include timing subcarriers andintegrated digital service subcarriers; and each of the subcarriers islocated at one of a plurality of evenly spaced frequency locations, withthe timing subcarriers being at locations +1 and −1, the upper tertiarysubcarriers being at locations +2 through +26, the lower tertiarysubcarriers being at locations −2 through −26, the upper mainsubcarriers being at locations +28 through +52, the lower mainsubcarriers being at locations −28 through −52, the upper backupsubcarriers being at locations +54 through +78, the lower backupsubcarriers being at locations −54 through −78, and the integrateddigital service subcarriers being at locations +27, +53, −27 and −53.27. The receiver of claim 25, wherein the subcarriers further includetiming subcarriers and integrated digital service subcarriers; and eachof the subcarriers is located at one of a plurality of evenly spacedfrequency locations, with the timing subcarriers being at locations +1and −1, the upper tertiary subcarriers being at locations +2 through+26, the lower tertiary subcarriers being at locations −2 through −26,the upper main subcarriers being at locations +28 through +52, the lowermain subcarriers being at locations −28 through −52, the upper backupsubcarriers being at locations +54 through +73, the lower backupsubcarriers being at locations −54 through −73, and the integrateddigital service subcarriers being at locations +27, +53, −27 and −53.28. The receiver of claim 25, wherein the subcarriers further includetiming subcarriers and integrated digital service subcarriers; and eachof the subcarriers is located at one of a plurality of evenly spacedfrequency locations, with the timing subcarriers being at locations +1and −1, the upper tertiary subcarriers being at locations +2 through+26, the lower tertiary subcarriers being at locations −2 through −26,the upper main subcarriers being at locations +28 through +52, the lowermain subcarriers being at locations −28 through −52, the upper backupsubcarriers being at locations +57 through +81, the lower backupsubcarriers being at locations −57 through −81, and the integrateddigital service subcariers being at locations +27, +53, −27 and −53.